This invention relates to a process for preparing aldols by catalytic reaction of aldehydes and/or ketones.
The preparation of aldols by reacting aldehydes with themselves or with other aldehydes, reacting aldehydes with ketones or reacting ketones with themselves or with other ketones using a basic catalyst is a standard reaction of organic synthesis. These reactions are therefore also referred to in general as aldol reactions (cf. ORGANIKUM, 18th EDITION, DVW, BERLIN 1990). The chemical industry also utilizes the aldol reaction, for example for preparing acetaldol from acetaldehyde (cf. ULLMANN""S ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY, SIXTH EDITION, 1999 ELECTRONIC RELEASE). The aldol reaction can be followed by a dehydration of the aldol to form an unsaturated aldehyde or ketone.
Prior art processes comprise various restrictions with regard to the conduct of the reaction. First, the maximum reaction temperature can be limited by the lowest boiling temperature of one of the components when an atmospheric operation is practiced. This limits the reaction rate and hence also the space-time yield; longer residence times can reduce the selectivity. There are also restrictions due to the heat removal performance of the apparatus used and due to safety engineering aspects of the exothermic reaction. These include for example a slow rate of metering or the use of a small quantity of catalyst. In these cases too the reaction rate and hence also the space-time yield is restricted and the selectivity impaired.
It is an object of the present invention to provide an aldol production process providing an improved space-time yield, conversion or selectivity or less costly alternatives.
This object is achieved according to the invention when, in a process of the type mentioned at the outset, the reaction is conducted in the channels of a microstructured reaction system.